The role of herbivores in the grassland carbon budget for Three-Rivers Headwaters region, Qinghai-Tibetan Plateau, China

Background: An accurate assessment of the carbon budget is a crucial part of projecting future climate change and its impact on ecosystems. Grasslands foster multiple ecological functions including support for wild animals and livestocks. Herbivores intake forage biomass carbon, then digest and metabolize, and finally retain some carbon. The carbon processes have not been well quantified, resulting in uncertainties in the estimation of regional carbon budgets for grassland ecosystems. Methods: An animal metabolic carbon flux model was developed for herbivores in the Three-Rivers Headwaters region of China. The forage intake and metabolic carbon rates were estimated through metabolic body weight and daily digested measures for the main herbivore species. Results: The carbon intake was 5.52TgCyear(-1) (45%) from partial aboveground biomass (12.2TgCyear(-1)), in which 39.31% was released into the atmosphere by respiration CO2, 43.77% was returned to the ecosystem as feces and urine, and 16.96% was retained in herbivores for population regeneration or for human well-being. Conclusions: This study, as the first research on this topic, quantified the carbon flux of herbivores and found livestock accounts for a major part of consumed carbon on grasslands, which is important for understanding regional carbon budgets to mitigate and adapt to climate change over grasslands worldwide.